The present invention relates to a tensioning mechanism for a safety belt reel-in mechanism, including a cable drive that is activatable in the event of a crash and includes a cable pulley that is adapted to be positively coupled with the belt reeling-in shaft of the reel-in mechanism via a locking member that is disposed on the cable pulley and is radially shiftable for engaging or meshing with coupling teeth provided on a toothed ring of the belt reeling-in shaft.
A tensioning mechanism of this general type is disclosed in U.S. Pat. No. 4,618,108, Butenop et al, issued Oct. 21, 1986. This known mechanism provides a locking member that is axially held on the cable pulley in an eccentrically mounted manner, and in the event of activation can be deflected radially against the force of a spring that loads the locking member in its rest position. When shifted radially, this locking member meshes via teeth in coupling teeth that are coupled with the reeling-in shaft of the belt reel-in mechanism and that extend about the cable pulley in the plane of the locking member that is mounted thereon, thereby producing a positive connection between the cable pulley and the belt reeling-in shaft of the belt reel-in mechanism. The mounting and mass ratios on the locking member are such that if the locking member is activated, the locking member lags behind the rotational movement of the cable pulley due to its inherent mass moment of inertia, and, due to its eccentric mounting, pivots radially outwardly. In so doing, the looking member is held in the plane of the coupling teeth by a spring that urges the locking member axially against the cable pulley, so that the cable pulley and the locking member that is pivotably mounted thereon are to be viewed as a functional unit.
Such a design of the coupling connection between the tensioning mechanism and the belt reel-in mechanism has the drawback that the teeth of the locking member turn at least partially out of the coupling teeth due to the mounting play that is unavoidable with regard to mounting of the cable pulley on a shaft journal or extension of the belt reeling-in shaft, and due to the verY high pulling force on the drive cable, which is related to acceleration and is particularly effective at the beginning of the tensioning movement directly after engagement or meshing of the teeth. As a result, the positive connection between the cable pulley and the belt reeling-in shaft that is initiated at the beginning of the tensioning movement under certain circumstances is again disengaged over the duration of the tensioning process.
With regard to mounting the cable pulley, together with the locking member that is disposed and held thereon, on the shaft extension of the belt reeling-in shaft, a free movement space for the cable pulley cannot be avoided in the event of load, with this space being composed of the bearing play proper, a certain flexibility of the shaft extension that is exhibited during loading, as well as a likewise occurring flexibility of the locking member teeth on the one hand as well as the coupling teeth on the other hand; added to this is a pitching moment or maximum torque of the cable pulley about the shaft extension, which is brought about by the fact that the line of application of the pulling force that acts on the drive cable, and the effective plane of the positively intermeshing teeth, are spaced from one another by a distance that manifests itself as a lever arm.
As a result of these influences, after an initially effected engagement of the locking member teeth in the coupling teeth, a torque occurs that preferably acts about that engagement tooth that is disposed at the greatest distance from the line of application of the cable-pulling force, and that, starting with that engagement tooth that is disposed the closest to the line of application of the cable-pulling force, turns the teeth of the locking member out of engagement with the coupling teeth, whereby the cable pulley yields to this torque, by deflecting, as a result of the aforementioned free movement space, so that the teeth of the locking member and the belt reeling-in shaft ultimately disengage.
It is therefore an object of the present invention to improve a tensioning mechanism of the aforementioned general type in such a way that a more reliable engagement of the teeth of the locking member and the coupling teeth of the belt reeling-in shaft is assured during every phase of the tensioning movement.